The present invention relates to coating compositions based on polymers having active hydrogen groups (particularly hydroxyl groups) which are cured with polyisocyanates. Although not limited thereto, these are particularly adapted for automotive refinish applications. Utility for other types of coating applications is also contemplated.
It is desirable to provide coating compositions that have excellent physical properties and appearance and also are formulated with minimal amounts of volatile organic content ("VOC"). This is especially true in the automotive coatings area where the finish of the automobile is a particularly important feature but is difficult to achieve with coating compositions having reduced amounts of organic solvents. In the automotive refinish coating area, there is the further requirement that the coating composition be capable of ambient temperature cure or at most a forced heating step with a slightly elevated temperature. Automotive clear coatings pose an additional challenge since the clear coatings must adhere well to the pigmented basecoats onto which they are applied.
In order to provide coating compositions with suitably low viscosity for application, for example, by spraying, while providing low VOC formulations, it has been necessary to resort to polymeric components of lower viscosity. For this purpose, suppliers of polyisocyanate curing agents have made available to the coating industry several low viscosity polyisocyanates that are useful as curing agents in conjunction with polymers having hydroxyl functionality or other functionality reactive with isocyanates. These include hexamethylenediisocyanate based materials and isophorone diisocyanate based materials. Using these materials, it has been found to be difficult to provide low VOC coatings with the combination of adhesion and rapid cure speed required for automotive refinish coatings. Another promising low viscosity curing agent is a triisocyanate derived from 4-aminomethyl-1,8-diaminooctane. This triisocyanate, informally known as triaminononane triisocyanate, is attractive because of its exceptionally low viscosity and low equivalent weight (84 grams per isocyanate equivalent). However, attempts to utilize triaminononane triisocyanate as the curing agent in coating compositions have heretofore been disappointing. More specifically, while it has shown a positive effect on adhesion, its effect on cure speed has not been favorable.
Accordingly, it would be desirable to be able to take advantage of the desirable characteristics of triaminononane triisocyanate without compromising other properties.